White lights in a triangular formation over a ridgeline drifting slowly and fading out ten seconds after I spotted them

It was a perfectly clear night. I looked NNW, standing at a bus stop in South Eugene, and I saw three white, slightly blurry lights drifting slowly to the right directly above the ridge line. They were apparently fixed together, or perhaps flying in perfect formation.

The lights looked to have size to them, not merely points of light like the stars in the background. It looked like a triangle seen nearly edge-on. It was relativelly flat. It looked to be as wide as a thumb's width at arm's length. It drifted at the speed of a bird flying for about ten seconds, fading out slowly, until it was gone.